The body breaks down most carbohydrates from the foods we eat and converts them to a type of sugar called glucose. Glucose is the main source of fuel for our cells. After eating, the time it takes for the body to convert carbohydrates and release glucose into the bloodstream varies, depending on the type of carbohydrate and the food that contains it. Some carbohydrate-containing foods cause the blood glucose level to rise rapidly; others have a more gradual effect. The glycemic index measures how fast and how much a food raises blood glucose levels. Foods with higher index values raise blood sugar more rapidly than foods with lower glycemic index values do.